Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$74.94	4.846%	$78.5716	$78.57	$78.55	$78.60
Purchase #2	$185.81	5.577%	$196.1726	$196.17	$196.15	$196.20
Purchase #3	$96.26	3.451%	$99.5819	$99.58	$99.60	$99.60
Purchase #4	$229.49	11.610%	$256.1338	$256.13	$256.15	$256.10
Purchase #5	$237.27	5.429%	$250.1514	$250.15	$250.15	$250.20
Purchase #6	$118.61	7.402%	$127.3895	$127.39	$127.40	$127.40
Purchase #7	$213.26	8.547%	$231.4873	$231.49	$231.50	$231.50
7 purchase totals =	$1,155.64		$1,239.4881	$1,239.48	$1,239.50	$1,239.60